Cathode-ray tube



Sept 10, 1957 H, R, McQUlLLEN ETAL .2,806,162

CATHODE-RAY TUBE Filed Aug. 18, 1954 IN I/ EN TOR.;

United States Patent O CATHODE-RAY TUBE Howard R. McQuillen and Robert J. Kistler, Lancaster,

Pa., assiguors to Radio Corporation of America, a corporation ol. Delaware Application August 18, 1954, Serial No. 450,731

6 Claims. (Cl. 313-64) This invention relates to improvements in cathode-ray tubes and has for its principal object to provide an improved color television tube wherein the maximum screen area is available for picture reproduction, and a tube characterized, in operation, by its substantial freedom from color dilution.

The color screen, or target, of a color kinescope comprises an orderly array of narrow phosphor lines, or small phosphor dots, arranged in groups of three colors, usually red, blue, and green. The target assembly includes an apertured shadow mask through which electrons travel as a beam in their transit to the tri-color screen. The particular line-like or dot-like color phosphor that is illuminated at any given instant is determined by the angle at which the scanning beam, or beams, passes through the apertured shadow mask and approach the screen. Should the beam, or electrons derived therefrom, strike a color phosphor other than one toward which the beam was originally directed, the purity of the color of the emitted light is adversely affected. This phenomenon is known as color dilution. Color dilution may appear to the observer either as a weakening of the selected color or as a hue of the same, or of another intensity, but of a different color, i. e. red or blue.

The present invention is applicable to kinescopes of both the line screen and dot screen varieties and is predicated upon an appreciation of the fact that color dilution may be attributed to the presence of stray electrons within the area circumscribed by the mask and screen assembly. The stray electrons may be either primary or secondary electrons reccted from the walls of the envelope when the electron beam, or beams, is over scanned and stray secondary electrons produced 4by this overscanning.

It has been observed that the principal sources of disturbing electrons are (l) electrons reflected from the boundary walls of the envelope when the beam, or beams, overscan, and (2) electrons retlected from the inner surface of the metal frame within which the screen and its mask are mounted. The effects of both of these sources of reliected electrons is minimized in accordance with this invention by the provision of an electron shield, which may also function as a support frame, adjacent to the periphery of the mask. Also, the mask may be deep drawn in accordance with this invention to provide a maximum available picture area. The electron shield is designed with an inside perimeter which is slightly smaller than the screen area whereby electrons retlected from the walls of the envelope, due to overscanning, are collected by the shield, while the entire picture area is available for picture reproduction. By means of the arrangement of the electron shield and a deep drawn mask, the maximum area in a given size tube is available for useful output signals.

The invention is described in greater detail in connecton with the accompanying single sheet of drawings in which:

2,806,162 Patented Sept. 10, 1957 ICC Fig. 1 is a transverse sectional view of a tri-color, kinescope constructed in accordance with the invention;

Fig. 2 is a perspective View of the screen assembly of the color kinescope of Fig. l;

Fig. 3 is an enlarged fragmentary elevational view of the screen unit of the color kinescope shown in Fig. 1, showing conventional patterns of mask apertures and color dots; and,

Fig. 4 is a greatly enlarged fragmentary sectional view of Fig. l.

Referring now to Figs. l and 4, a color kinescope tube 10 comprises an evacuated envelope 11 including a main chamber in the form of a frustum 12 the large end of which terminates in a window, or transparent face plate, 13. The small end of the frustum 12 terminates in a neck portion 14 which, in this case, contains a battery of three electron guns 15, 16 and 17 arranged 120 apart, and substantially parallel to the long axis of the tube 10. Surrounding the neck portion 14 is a conventional deection yoke 25 which produces a plane of deflection P-P for the electron beams. The point from which each electron beam is deliected, in the plane of deliection, is called the center-of-scan. The centers-of-scan are shown as dots in Figure l. As shown the envelope 11 is composed of glass. However, it should be understood that the envelope 11 could be made of a conducting material. Also, the envelope 11 is substantially rectangular in cross-section. Furthermore, this invention is applicable to color kinescopes utilizing only one electron gun.

In the enlarged end of frustum 12 there is shown a masked target 18 including red, blue, and green phosphor dots (see Fig. 3) which are arranged in a hexagonal mosaic pattern on the inner, or target surface, of the glass face plate 13 to form a screen 22. The glass face plate 13 may be of any desired shape, i. e. circular or rectangular, and curvature, i. e. spherical. In the instant case the glass face plate 13 is in the form of a rectangular section of a spherical shell. Alternatively, the color screen may comprise a i'lat glass plate (not shown) independently mounted behind the face plate 13.

Supported closely adjacent to the phosphor dot screen 22 is an apertured mask 23 which may be formed of a thin metal, or other conducting material. In the embodiment shown the mask 23 is deep drawn, which will be explained hereinafter, and is made of some type of conducting material. The conducting material for mask 23 maybe of a material having substantially a zero thermal coefcient of expansion over the normal operating temperatures of color kinescopes, an example of such a material is Invarf Also, conductive materials having other coefficients of expansion may be utilized and temperature compensating means employed. Examples of such other materials are carburized steel or aluminum. When, as in the instant case, the mask screen pattern is laid down directly on the curved face plate 13 of the envelope 11, the mask 23 is appropriately curved so as to be approximately concentric with the curved inner, or target surface, of the face plate 13.

In accordance with this invention the mask is deep drawn to provide a maximum of available picture area. By deep drawn is meant a mask having an apertured surface 27 which curves into side walls, or marginal edges, 28 on the long side of the rectangle and side walls, or marginal edges, 29 on the short side of the rectangle. The deep drawn type of mask is extremely useful in the process of manufacturing a color kinescope due to the fact that flat tools can be utilized during the processing and the scalloped border for the hold down pads is eliminated. Furthermore, the deep drawn mask may be made more rugged, and with less expensive means, since a llat support frame 26 may be utilized.

As is well known, the apertures 24 in the mask 23 are arranged in the same hexagonal pattern as the phosphor dots 19, 20, and 21 which are laid down on the face plate 13. ln the present case the apertures 24 are of circular contour with a constant separation between their centers. With such a hexagonal arrangement of apertures 24 the red, blue, and green scanning beams (see Fig. l) pass through their respective centers-of-scan in the plane of deilection P-P of the tube with the beamcenters equally spaced from each other and at a common distance from thc tube axis.

Surrounding the outer periphery of the formed mask 23 is an electron shield 26. The electron shield 26 is shown connected to the walls 28 and 29 of the formed mask 23 and may actually be a portion of the formed mask 23. Also, as shown, the shield 26 comprises a support frame, or plate, for the formed mask 23. The electron shield 26 is designed with an inner perimeter which just shields the electron beam, or beams, from the walls 2S and 29 of the formed mask 23 at any point around the mask.

The deep drawn mask 23 is shaped so that, assuming a 2l inch tube., the wall portions 28 along the long side are approximately l inch deep while the wall portions 29 along the short side are approximately one-half inch deep. As shown more clearly in Fig. 3 the wall portions 28 and 29 taper toward the corners of mask 23 and thus result in the curvature of the mask being substantially the same as the curvature of the face plate 13.

The inner periphery of electron shield 26 is Selected to permit thc entire apertured area of mask 23 to be scanned by the electron beam, or beams. Also, the selection of the size of the inner periphery of shield 26 includes a consideration of the angle of reilection of primary electrons reflected from the walls of envelope 11, and the paths of secondary electrons dislodged therefrom. As shown more clearly in Fig. l the inner periphery of mask 26 is selected to intercept the electrons reflected from the walls of envelope 11. In other words, the shield 26 extends inwardly to a point substantially on a line between the center-of-scan and the outermost aperture in mask 23.

The electron shield 26 may be formed as a part of mask 23 or may he a flat angular metallic member, as shown, which functions not only as an electron shield but also as a support, or frame, for the balance of the mask 23.

The mask 23 may be supported within the envelope 11 by a means of support pins 31 which are embedded in the glass envelope. lf a metallic envelope is utilized, the mask may be supported by being welded to support pins which are in turn welded to the walls of the envelope.

The deep drawn mask 23 may be formed by drawing the mask in a press set (not shown) utilizing a male die having a contour approaching that desired in the drawn part of the mask. The male portion of the die set presses the mask into a conned rubber pad. The contour and shape of the male die is determined by the kinescope bulb geometry and will have to deviate slightly from the desired design to correct for spring back in the drawn mask material. A pressure pad is necessary; it should consist of a ring holding down the periphery of the mask. The pressure pad maintains tension in the mask during the draw and prevents the mask from wrinkling. Complex mask contours may be more easily accomplished utilizing two or more draw operations, in which case a sequence of male dies is required.

What is claimed is:

l. A cathode-ray tube comprising an evacuated envelope, a substantially rectangular fluorescent screen supported within one end of said envelope, electron gun means adapted to project at least one electron beam onto said screen, an electrode within said envelope and between said screen and said gun means, said electrode comprising an apertured portion disposed adjacent to said screen and in the path of said beam and four marginal edge portions, said apertured portion being substantially rectangular in shape, each of said marginal edge portions comprising a member extending along the inner surface of said envelope approximately parallel to the walls of said envelope.

2. A cathode-ray tube as in claim l further comprising an imperforate shielding means extending along said means intermediate said electron gun means and said marginal edge portions effective to prevent substantial bombardment of said marginal edge portions by said beam.

3. A cathode-ray tube comprising an evacuated envelope, at least one beam source of electrons in one end of said envelope, a target assembly Within the other end of said envelope comprising a rectangular viewing screen having a spherical surface and an apertured conductive mask, said screen being supported on the inner surface of said other end of said envelope and substantially covering said inner surface, said mask comprising a rectangular apertured portion having a spherical surface supported closely adjacent to said inner surface and wall portions extending from said apertured portion along said envelope toward said beam source of electrons and a shield portion, said shield portion extending from closely adjacent to the walls of said envelope to points inwardly of said Wall portions and substantially normal to the path of said beam whereby only the apertured portion of said mask is struck by electrons and electrons reflected from said envelope walls are collected by said shield portion.

4. A cathode-ray tube comprising an evacuated envelope containing a beam source of electrons, a target assembly comprising a rectangular viewing screen having a spherical surface and an apertured conductive mask through which said beam passes in its transit to said screen, said screen being supported on an inner surface of said envelope, the apertured portion of said mask being of substantially the same configuration as said inner surface and spaced closely adjacent thereto, four marginal edge portions of said mask each extending from said apertured portion back toward said beam source, and an apertured electron shield supported on said marginal edge portion, the inner periphery of said electron shield being smaller than the area of said screen whereby said screen is bombarded by substantially only primary electrons directly from said source.

5. A cathode-ray tube as in claim 4 wherein said electron shield is supported near the end of said envelope supporting said screen.

6. A cathode-ray tube comprising an evacuated envelope containing a beam source of electrons, a target assembly comprising a rectangular viewing screen having a spherical shape and an apertured conductive mask through which said beam passes in its transit to said screen, said screen being supported on an inner surface of said envelope, the apertured portion of said mask being of substantially the same configuration as said inner surface and spaced closely adjacent thereto, marginal edge portions of said mask extending from said apertured portion back toward said beam source, and an apertured electron shield supported on said marginal edge portions, the inner periphery of said electron shield bcing smaller than the area of said screen whereby only electrons in their transit directly from the center of deflection of said tube strike the active areas of said mask which are adjacent to areas of said screen.

References Cited in the le of this patent UNITED STATES PATENTS 2,580,697 Oliver Jan. 1, 1952 2,611,100 Faulkner et al Sept. 16, 1952 2,682,620 Sanford .Tune 29, 1954 2,690,518 Fyler et al. Sept. 28, 1954 

